168 



HORN LOUD SPEAKERS 



coupled to a common throat, Fig. 8.18. The directional characteristics 

 of this type of loud speaker were discussed in Sec. 2.9. Figure 8.18 shows a 

 12-cell high frequency unit. The throat is coupled to one or more mech- 

 anisms depending upon the power requirements. 



An electric filter or dividing network is used to allocate the power to the 

 high and low frequency units. The filter introduces phase shift as well as 

 a loss in power of 2 or more db. 



The efficiency characteristics of the high and low frequency units of this 

 loud speaker without the filter are shown in Fig. 8.15, characteristics B and A. 



C. Compound Horn Loud Speaker"^^. — The compound horn loud speaker 

 consists of a single diaphragm mechanism with one side of the diaphragm 



SECTION B-B 



l^ffwHhE]" 





EQUIVALENT CIRCUIT 



FRONT VIEW 



SECTION A-A 



1000 

 FREQUENCY 



Fig. 8.19. Cross-sectional view of a compound horn loud speaker, the developed equivalent 

 of the high and low frequency horns, and the equivalent circuit of the acoustical system. 

 The sections A-A and B-B refer to the horizontal and vertical cross sections of the front 

 view. The graph shows the frequency ranges of the high frequency and low frequency 

 horns and the overall pressure response characteristic. 



coupled to a straight axis horn and the other side coupled to a long folded 

 horn. Fig. 8.19. The equivalent of the system is shown in Fig. 8.19. The 

 functional equivalent circuit of the vibrating system is shown in Fig. 8.19. 

 At the low frequencies the reactance of the acoustic capacitance Ca2 is 

 large compared to the throat acoustic impedance of the low frequency horn 

 and sound radiation issues from the low frequency horn. At the high fre- 

 quencies the reactance of the acoustic capacitance Ca2 is small compared 



Olson and Massa, Jour. Acous. Soc. Amer., Vol. 8, No. 1, p. 48, 1936. 



